Like it was said previously I don't think anyone has doubts about the boost converter, and keeping a constant 1.5V.
Now the video regarding the "fleshlight" has brought another point. By definition using a flashlight means you walking in darkness or needing some light. Using the batteriser means you can have constant light and going into darkness suddenly. I think I would prefer extra time with a small amount of light, then consuming everything and using ecolocation to navigate after that.
What happens if you are in a forest and need to get back, I prefer extra time with a small amount of light, than spending the night there. Or if you are in a cave, again extra time wins. So even the flashlight example is wrong, by definition I need light, the longer the better.